The invention relates to an antenna arrangement in which at least two frequencies can be transmitted by means of a single antenna.
In the mobile radio communication field, there is a need to be able to transmit signals in different frequency bands. Furthermore, it is desirable, in satisfying this need, to be able to use a single antenna arrangement. An antenna arrangement for transmitting AM/FM and microwave, is described in U.S. Pat. No. 4,968,991. The solution described in U.S. Pat. No. 4,968,991 can, at most, be utilised for frequencies up to 3 GHz. This antenna arrangement also comprises inner and outer conductors and tubes.
The requirement for transmitting several frequencies in, for example, mobile radio traffic, is combined with the requirement of speech communication and, respectively, the transmission of traffic information. It is intended to transmit traffic information in a higher frequency band than the one utilised for normal radio communication.
It is possible to arrange different antennas for different frequencies. These antennas can be placed, for example, on the roof of a vehicle, such as a car, on its rear view mirrors, or at the front of the vehicle. When microwaves are transmitted by an antenna, it is desirable that the range is limited. This can be done, for example, by mounting the antenna element at the front of the vehicle. One difficulty with such an arrangements is that both the antenna element and the feed line for the antenna element become soiled by dirt, and the like, from the roadway. Soiling causes shielding of the radio waves and thereby gives rise to impaired transmission efficiency for the antenna. There is, therefore, a requirement for an antenna arrangement for vehicles, which is not affected by dirt from the roadway.
It is considered that frequencies in the GHz range are suitable for the transmission of traffic information. The relevant frequency ranges are of the order of 10 GHz and higher.
It is an object of the present invention to provide an antenna arrangement for simultaneously transmitting UHF and the X and K frequency bands utilizing a single coaxial antenna arrangement. Antenna arrangements adapted for transmission in the 10 GHz frequency range have not, hitherto, been available.